Scientists have developed new “fluorogen activating proteins” that will become a key component of novel molecular biosensor technology. The FAPs can be used to monitor biological activities of individual proteins and other biomolecules within living cells in real time. Researchers designed the FAPs to emit fluorescent light only when bound to a fluorogen, an otherwise non-fluorescent dye added by the scientists. This feature will allow biologists to track proteins on the cell surface and within living cells in very simple and direct ways, eliminating cumbersome experimental steps.